Saturday, February 14, 2015

Stress and hunger - The connection holds, particularly in the evening hours, being stressed may turn you into a fridge raider.

I have to say that the scientific journal Appetite published by Elsevier is becoming one of my favorite sources for relevant research on the actual grounds of the obesity epidemic, which are quite obviously of both physiological and psychological nature.

I've selected a handful of the latest in press articles, which are about to appear in one of the future issues, for you to satisfy your craving for the latest nutrition research on the time-course of the stress => hunger cascade, the acute and 24h effects of aerobic exercise on total and relative energy intake and the surprisingly negative correlation between the sweetness threshold for aspartame and energy intake.

Learn more about the effects of your diet on your body composition at the SuppVersity

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Stress takes it's binge-triggering toll mostly in the evening - We've known for decades that there is a link between perceived stress and hunger.

Figure 1: Graphical summary of slope function within a day. The Y-axis represents the magnitude of momentary association between perceived hunger and stress and the X-axis represents time of day (Huh. 2015)

What we didn't know, though is the exact time-course of this association.

In their latest scientific study, scientists from the University of Southern California and other research centers monitored the association of perceived stress and hunger continuously over a week in free-living individuals (Huh. 2015). To this ends, they recruited 45 young adults (70% women, 30% overweight/obese) ages 18 to 24 years (Mean = 20.7, SD = 1.5), with BMIs ranging from underweight (17.4 kg/m²) to obese (36.3 kg/m²) and had them rate / measure their stress levels and hunger and food intake on more than 500 occasions over a 7-day period via text messaging assessments and real-time eating records.

The scientists used a time-varying effect modeling was used to explore whether the within-day fluctuations in stress are related to perceived hunger assessed on a momentary basis and found that there is (a) a generally positive stress–hunger relationship was confirmed, but that (b) the strength of the relationship was not linear.

"Rather than the magnitude of the association between perceived stress and hunger changed throughout the day such that only during specific time intervals were stress and hunger significantly related. Specifically, the strength of the positive association peaked during late afternoon hours on weekdays (β = 0.31, p < .05) and it peaked during evening hours on weekend days (β = 0.56, p < .05)" (Huh. 2015).

Practically speaking this means that people tend to react to stress with (over-)eating mostly during the evening hours. When they are at work in the office or wherever else they may be working being busy probably suppresses the perception of hunger and thus their risk of binging on whatever is in sight.

For you as a highly stressed inhabitant of the 21st century, destressing and binge control in the evening hours may thus be of primary importance to curb your tendencies to ruin all your diet efforts upon sundown.

Exercise has different effects on food intake in active and inactive pre-menopausal women - While the food intake on the meal immediately after a low intensity cardio session increased for both, researchers from the Trinity College Dublin observed a significant, but delayed reduction in energy intake in inactive, but not active women.

Rocha et al. examined the effects of an acute bout of exercise of low-intensity on food intake and energy expenditure over four days in women taking oral contraceptives. Twenty healthy, active (n=10) and inactive (n=10) pre-menopausal women taking oral contraceptives completed two conditions (exercise and control), in a randomised, crossover fashion. The exercise experimental day involved cycling for one hour at an intensity equivalent to 50% of maximum oxygen uptake and two hours of rest. The control condition comprised three hours of rest.

Participants arrived at the laboratory fasted overnight; breakfast was standardised and an ad libitum pasta lunch was consumed on each experimental day. Participants kept a food diary to measure food intake and wore an Actiheart to measure energy expenditure for the remainder of the experimental days and over the subsequent 3 days.

Figure 3: If you consider intake and expenditure working out still lead to a reduction of the overall energy balance and would thus help to support the women's dieting efforts (Roa. 2015).

There were no significant differences in energy intake over the four days in active participants, but there was a suppression of energy intake on the first day after the exercise experimental day compared with the same day of the control condition in inactive participants (mean difference = -1974 kJ; 95% CI -1048 to -2900 kJ, p = 0.002, d = -0.89).

There was a group effect (p = 0.001, d = 1.63) for free-living energy expenditure, indicating that active participants expended more energy than inactive participants during this period. However, there were no compensatory changes in daily physical activity energy expenditure (see Figure 3). Thus, Roa et al. are right, when they say that their "results support the use of low-intensity aerobic exercise as a method to induce a short-term negative energy balance in inactive women taking oral contraceptives" (Roa. 2015). For those who are not sedentary coach potatoes, though, previous research indicates that high intensity cardio and or lifting are the preferred modes of exercise when it comes to appetite suppression.

Your Aspartame threshold negatively predicts your energy consumption - That sounds crazy, but it is the main result of a recent study from the Universidad de Guanajuato in Mexico.

As a SuppVersity reader you know that the overwhelming majority of clinical human trials shows that artificially sweetened foods promote, not hinder fat(!) loss. Sorensen, et al. for example recorded a loss of 1.2kg body fat in 70 days in subjects who consumed artificially sweetened products instead of their regular counterparts | more.

In an experiment, Martinez-Cordero et al. assessed the perception in normal and overweight mexican adults. While they found no clear association between any of the primary perception taste thresholds with energy intake or BMI, the authors report that

"the perception threshold of aspartame was negatively associated with energy intake.he perception threshold of aspartame was negatively associated with energy intake" (Martinez-Cordero. 2015).

That's a surprising yet quite significant finding that stands in contrast to what the scientists had expected based on previous studies of which many found that obese adults reported liking intensely sweet solutions (Drewnowski. 1997) and the notion that consuming intense sweeteners may trigger increases in appetite and thus promote the development of obesity.

As the authors point out it does thus remain unclear as to how taste perception and sensitivity contribute to the excess energy intake associated with obesity. Additional research on the question of how taste sensitivity may drive specific food preferences is warranted.

Odds ratio and 95% CI of frequency of family meals, weight status, and healthy management by age group, adjusted for age, BMI, and socio-economic status (Nuvoli. 2015).

Last but not least: Being Italian does not exactly prevent you from getting obese. While the obesity rate in the US is still significantly higher than in Sardinia, the Italians aren't only catching up, according to a recent study (Nuvoli. 2015) 50% of them don't even realize that they are significantly overweight. In that, the fact that they still have a significantly higher frequency of dinner in the family compared to people in other countries does not seem to have an obesity preventive effect - that's at least what the latest data from the University of Sassari would suggest.

Without stress reduction and exercise, the inhabitants of the purported homeland of pizza, pasta and the Mediterranean Diet are thus not better off than their similarly obese European neighbors.

What may be worth mentioning, though is that people who eat frequent family meals were a bit more likely to be normal weight, mostly not dieting and rated their appetite as normal. Information on the amount of exercise and the "aspartame threshold", the critical correlates of energy consumption in the studies by Rocha, et al. and Martinez-Cordero, et al., is unknown, though | Comment on Facebook!

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